In the data processing system art, it is often desirable to be able to protect an entire system or selected portions of a system from accesses which are defined as unauthorized. As an example, an unauthorized access may be either a read access, a write access, or both types of accesses to a memory storage device storing program or data information used by the data processing system. In some data processing systems an unauthorized access may be defined as an access to a particular resource, such as a port on a micro controller integrated circuit, that is used to access one or more external integrated circuit terminals. In yet other data processing systems, an unauthorized access may be defined as an access to a particular resource of the data processing system, such as debug circuitry or timing circuitry. Regardless of the resource to be protected, an improved approach to protecting against unauthorized accesses was desired.